Diffraction Optical Element Pitch Alignment for Display Brightness
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Solution Overview
Problem
Display devices using diffraction optical elements face issues with brightness unevenness and color shifting due to varying diffraction efficiency across different viewing angles, particularly when miniaturizing and thinning these devices, as the diffraction efficiency changes with the angle of incidence and wavelength, leading to inconsistent image quality.
Innovation Solution
The implementation of a display device with an image forming unit and an optical system that includes a first diffraction optical element with a pattern where the pitch direction coincides with the narrow aspect of the image, using reflection-type volume holograms as diffraction optical elements to guide light while maintaining angular information and ensuring high transparency, allowing for simultaneous viewing of the external scene and the image.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a diffraction optical element is used to guide light in a miniaturized display device, then the device can be thinned and miniaturized, but brightness unevenness and color shifting occur due to varying diffraction efficiency across different viewing angles
Solution Approach 1:
The patent applies local quality by making the pitch of the diffraction pattern non-uniform across the optical element surface. Specifically, the pitch is adjusted locally in different regions to compensate for the varying angles of incidence, ensuring that diffraction efficiency remains consistent across the entire field of view. This local adjustment of pitch creates regions with different diffraction characteristics tailored to their specific viewing angles.
Solution Approach 2:
The patent changes the physical parameter of the diffraction pattern pitch to resolve the contradiction. By varying the pitch parameter across the diffraction optical element surface, the system maintains optimal diffraction efficiency for different viewing angles while keeping the device miniaturized. This parameter modification allows the same optical element to serve multiple angular zones effectively.
2Illumination intensity
If the pitch direction of the diffraction pattern is aligned with the narrow aspect of the image, then brightness and color unevenness are suppressed, but the device complexity increases due to precise alignment requirements
Solution Approach 1:
The patent applies asymmetry by intentionally misaligning the diffraction pattern pitch direction relative to the image aspect ratio. Instead of perfect alignment, the pitch direction is set at a specific angle (e.g., 45 degrees) to the image width direction, creating an asymmetric configuration that naturally balances the diffraction efficiency across different spatial frequencies and viewing angles, thereby suppressing brightness and color unevenness.
Solution Approach 2:
The patent introduces dynamic adaptability by making the pitch direction and pitch value adjustable or selectable based on the specific application requirements. This allows the system to optimize the balance between brightness uniformity and alignment complexity dynamically, rather than being fixed at a single configuration.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration suppresses brightness and color unevenness by optimizing the diffraction efficiency and maintaining image quality, enabling the miniaturization and thinning of the display device while ensuring consistent image display across different angles and wavelengths.
Implementation Method 1
a first diffraction optical element having a pattern that diffracts light and configured to deflect the image light in the optical system
Implementation Method 2
the light guide unit guides incident light inside of the light guide unit while the incident light repeats total reflection
Data Source
AI summary
In a display device, an image having an aspect not equal to 1 is formed by an image forming unit configured to form an image, and the image is guided as an image light to a display position by an optical system. The optical system, which is provided with a diffraction optical element, deflects the image light. In the diffraction optical element, a pitch direction of a pattern for deflecting the image light coincides with a direction in which the aspect of the image is narrow. In the display device, the direction in which the image light is deflected by the diffraction optical element coincides with the direction in which the aspect of the image formed is narrow, thus making it possible to suppress unevenness of brightness and hue within a plane of an image displayed.